function getMd5(file,callback){
        var blobSlice = File.prototype.slice || File.prototype.mozSlice || File.prototype.webkitSlice,
        chunkSize = 2097152,                             // Read in chunks of 2MB
        chunks = Math.ceil(file.size / chunkSize),
        currentChunk = 0,
        spark = new SparkMD5.ArrayBuffer(),
        fileReader = new FileReader();

    fileReader.onload = function (e) {
        spark.append(e.target.result);                   // Append array buffer
        currentChunk++;

    if (currentChunk < chunks) {
        loadNext();
    } else {
        callback(spark.end());  // Compute hash
    }
};

    fileReader.onerror = function () {
        console.warn('oops, something went wrong.');
    };

    function loadNext() {
        var start = currentChunk * chunkSize,
        end = ((start + chunkSize) >= file.size) ? file.size : start + chunkSize;

        fileReader.readAsArrayBuffer(blobSlice.call(file, start, end));
       }
    loadNext();
}